I've had trouble recently with my 05 Silverado 5.3L intermittently idling rough and running rough at low engine speeds. The check engine light came on and the exhaust smelled bad. I got the codes PO131, PO171, PO300 which suggest a lean condition on the left bank. However when I pulled the spark plugs, all the plugs on the left bank looked rich and the ones on the right looked normal. Well I disconnected the left front (pre-cat) O2 sensor and drove it today and it runs fine now although it does turn on the check engine light since the O2 sensor is disconnected. It appears that the O2 sensor was giving a false lean signal and the computer was over richening the left bank to try to compensate. So I'm going to install a new sensor tomorrow. I'm glad it wasn't a cracked intake.

I've had trouble recently with my 05 Silverado 5.3L intermittently idling rough and running rough at low engine speeds. The check engine light came on and the exhaust smelled bad. I got the codes PO131, PO171, PO300 which suggest a lean condition on the left bank. However when I pulled the spark plugs, all the plugs on the left bank looked rich and the ones on the right looked normal. Well I disconnected the left front (pre-cat) O2 sensor and drove it today and it runs fine now although it does turn on the check engine light since the O2 sensor is disconnected. It appears that the O2 sensor was giving a false lean signal and the computer was over richening the left bank to try to compensate. So I'm going to install a new sensor tomorrow. I'm glad it wasn't a cracked intake.

I just thought this may help someone experiencing the same problems.

Which sensor is it? I've got 2 new rear ones that came off of the motor I put in my burb. Let me know, maybe we can work a partial trade on those covers, .

I think all the sensors are the same,I know the 6.0 vans are. The o2s are caausing alot of running rought and code po300 codes. We have a fleet account at work and there trucks and vans are coming in at least once a week for this.